Among human parents there is a bias for holding infants on the left side of the body. This left-side bias is also present in our closest phylogenetic relatives , the great apes. This bias may represent an underlying specialization of the right hemisphere for interactions with very young infants, and may therefore play a role in the formation of attachment between parent and offspring. One purpose of the present study is to determine if this (possible) homology extends to old world monkeys, in this case rhesus macaques. Another goal is to determine if there is a relationship between lateralized holding of infants, early mother-infant interactions, and later social development of infants. Rhesus mother-infant pairs housed in field cages N2 and N3 have been observed. Pilot studies conducted during June-September 1993, from which information regarding the context and quality of mother-infant interactions was obtained, were used to formulate a method to examine relational and lateralized aspects of behavior. The following categories of behavior are used to assess the quality of relationship, as well as lateral biases nursing, restraint, retrieval, antagonism, physical support while clinging, and manual investigation. Longitudinal data will shed light on the development of social relationships as an infant expands its interactions with its social environment. Male and female rhesus infants born to high, middle and low ranking mothers are being observed from birth to 2 months of age, at 6 months, and again at 10-12 months. Mother-infant interactions are the focus of the earliest observations, and later observations will include interactions with siblings, peers, and other adults.